The invention relates to an electrostatic drive device in which the voltage of one or more electrodes is controlled to generate electrostatic force, which produces relative movement between two or more objects to which the electrodes are secured.
Use of electrostatic forces to control movement occurring between a pair of objects is known. One way of accomplishing this is by affixing or forming electrodes on a pair of objects, and applying voltages to the electrodes in order to generate electrostatic force. By taking into account the details of the physical connection between the objects, the voltages and resulting electrostatic force may be manipulated to control the resulting movement between the objects.
In micro electro-mechanical systems (MEMS), it is often necessary to effect very small, precise movements between objects through a range of motion. To do this, sometimes a large number of electrodes are used, with the individual electrodes being spaced closely together, say a few micrometers or less. In some cases, resolution enhancement (i.e., finer movement steps) may be had by further decreasing the pitch, or spacing, between adjacent electrodes. This is not feasible, however, where the pitch is already at or approaching the limits of what is possible with a given fabrication technique. In other cases, it may be disadvantageous to increase the electrode density, even though technically possible. For example, increased electrode density may consume extra space, increase heat output, or require undesirably complex supporting electronics.
Regardless of the size or quality of the relative movements, it is normally desirable that the movements be easy to control. Many prior systems fail in this regard. Some are difficult to control because they are not designed in a way that allows them to be easily incorporated into a closed loop control system. Other systems require use of complicated protocols or command languages to produce the desired movements. Still others require that the operator of the system have a detailed knowledge of the mechanical details of the system in order to create the necessary voltages and electrostatic forces necessary to create the relative movement.
The present invention provides an electrostatic drive having a mover with a plurality of mover electrodes operatively affixed thereto, and a stator with a plurality of stator electrodes operatively affixed thereto. The mover and stator are movable relative to one another via electrostatic force generated between the mover electrodes and the stator electrodes. The electrostatic drive includes a driver configured to drive the stator electrodes into any of a plurality of sequential voltage states, where each voltage state is defined by a combination of LO and HI voltage levels at the stator electrodes. Transition from one voltage state to a sequentially adjacent voltage state produces a step size of relative movement between the mover and stator. For each of the sequential voltage states, the driver is further configured to selectively vary voltage applied at one of the stator electrodes to an amount between the LO and the HI voltage levels, in order to produce a proportionally smaller step size and thereby increase resolution of the electrostatic drive.